Games crashing to desktop

Hello everyone. I`m having problems with my games & internet browsers. Games always crash to desktop. Firefox & Google Chrome crashes when i load too many pages. I recently changed my gfx card from INNO3D 8600gt to an XFX 9800gt & from 2x512mb ddr 400 ram, i upgraded to 2x1gb ddr 400 ram sticks. I thought i had an insufficient coolermaster 380w psu, so i changed it to a silverstone 500w psu. I still had the same problem after i changed my psu. All worked well before i upgraded my gfx card, ram & psu.

I`ve run them all overclocked & at stock settings & still the problem persists. I've ran memtest & Vista`s memory diagnostic tool? & no problems were found with my rams.

The games that always crash are, L4D (in singleplayer, crashes anytime & if i make it through like 5-10 mins of the game, crashes mostly when mob attacking), C&C RA3 (campaign, anytime), Hitman Bloodmoney (crashes anytime) & the Fear 2 demo (crashes anytime).

2 PFN_list_corrupt bsods occured so far from my last reformat around 7 Feb 09. I've tested old to new drivers, still the same. Currently using all latest drivers & DirectX. I'm using a coolermaster hyper tx2 for my cpu, stock cooling on gfx card & 2 case fans.